DESCRIPTION: (Applicant's Description) New therapies and preventions under investigation to reduce the threat of prostate cancer will not help patients who must be treated with present modalities. Improvements to radiotherapy, a proven therapy, are essential. Measured doses in patients will reduce uncertainty and lead to more individualized therapy. Permanently implanted radiation dosimetry seeds (RDS) can be interrogated remotely to yield signals reflecting the local radiation exposure. Prototype systems suitable for seed implants were constructed and evaluated for sensitivity to radiation, accuracy, and stability. Experiments established that accumulated doses of greater than 70 Gy can be measured to a sensitivity of 1 Gy, or better. Verification of the dose by RDS assures accuracy of the computed distribution and provides a record of the treatment. RDS would reduce uncertainty in complex conformal therapy, in brachytherapy and in critical normal structures. High density markers can be detected with portal images produced from therapeutic energy beams and so, in conjunction with treatment planning, can be used to better target the radiation. Three seeds could establish a field edge precisely for tumors near critical organs. Combining the two concepts, Marker RDS permit image guided therapy with measured doses.